Effects of potassium on methanol adsorption and dissociation on â-Mo2C(001). A DFT study on a model surface

C. PISTONESI, A. JUAN, A. P. FARKAS, F. SOLYMOSI

Ankara

Conferencia; 13th European Conference on Applications of Surface and Interface Analysis; 2009

Dept. of Chemistry, Bilkent University

The adsorption and dissociation of methanol on â-Mo2C(001) surface was studied using density functional theory calculations. We modeled the bulk and the Mo-terminated carbide surface using a four layer slab. Methanol is adsorbed with the OH group pointing towards the surface. The computed adsorption energy for methanol on Mo2C results -37.8 kJ/mol, which is in excellent agreement with the value of 37 kJ/mol measured from Temperature Programmed Desorption 1. The surface withdraws charge from the molecule making it more negative in such a way that the molecule becomes positively charged as a whole, creating a positive outward dipole moment. A similar result was experimentally determined in the case of methanol and ethanol on Mo2C 2,3 from changes in the work function.  The formation of the methoxy specie is energetically favorable after H abstraction. The bonding analysis using the crystal orbital overlap population (COOP) curves shows a Mo-Mo weakening upon adsorption and a strong H-Mo interaction after dissociation. The effect of K was also analyzed simulating a low K coverage on the surface. We obtained that the most favorable adsorption site for methanol is on top on K atom. Although adsorption energies are similar than on the clean surface, our results suggest that a different dissociation mechanism for methanol is produced when K is present on the surface.